Peelably laminated containers made of synthetic resins are known and obtained by peelably laminating an outer layer that forms an outer shell of a finite shape and an inner layer that forms a deformable inner bag. These blow-molded bottles are generally referred to as delaminated bottles.
An outer parison and an inner parison having no compatibility with each other are first extruded together to give a laminated parison. This laminated parison is then blow-molded into the peelably laminated synthetic resin container by using a split mold for blow molding. At that time, the bottom portion is pinched with the pinch-off of the blow mold and is pressed flat to form a bottom seal. Since the bottom seal has basically a laminated structure consisting of the outer layer and the inner layer, which are not compatible with each other, there was dissatisfaction in that the outer layer is easily cracked at the bottom.
As a conventional art to relieve this dissatisfaction, there is Japanese Laid-Open Patent Application No. 1996-216238. In the configuration of that invention, the bottom portion is pinched with the pinch-off of the blow mold and is pressed flat to form the bottom seal, as described above, but the seal is overlaid with a pair of ribs and pressed together so that a ridge is formed along the parting line. Some interlocks are provided at several points along the seal as both ribs bite into each other.
In this conventional art, the bottom seal is formed into a ridge having a certain height and width. As a result, the bottom seal has a large area of pressed contact between the outer layer and the inner layer. The interlocks provided at several points not only increase the area of pressed contact further, but also increase resistance to the shearing force that is parallel to the plane of pressed contact, thereby making it possible to obtain a bottom seal having a mechanical strength that is high enough to prevent the bottom seal from cracking.
However, in the above-described conventional art, there are cases of cracking in the bottom seal because of the effect of time-lapsed shrinkage at the bottom, which takes place after the containers have been blow-molded. The problem of bottom cracking is often found especially in large-size containers of this conventional art when they are dropped onto the floor or when they experience a shock.
Therefore, the blow-molded containers of this kind are required to go through complete cool-down and shrinkage within the mold. A problem arises here because the bottom seal has large height, thickness, and cubic volume, which need long hours of cooling and thus result in quite low efficiency in the production of containers.
This invention has been made to solve the above-described problem. The technical problem of this invention is to achieve strong adhesion between the outer layers at the bottom seal without increasing the bulk of the bottom seal. The object of this invention is to provide a peelably laminated, blow-molded synthetic resin container having higher strength and greater economic efficiency at higher manufacturing efficiency than ever, without causing a decrease in the ability of the container to sit on the bottom.